This invention relates generally to the distribution of conditioned air and deals more specifically with an air distribution system which is specially arranged to deliver conditioned air to hospital patient rooms, research laboratories, or industrial clean rooms.
The heating and cooling of most large buildings is achieved by heating or cooling air and passing the conditioned air through ventilating ducts that extend throughout the building. Individual temperature control of each separate room is desirable and is usually accomplished by equipping each duct or each terminal unit with a flow control device such as a damper. Each flow control device can be individually controlled to adjust the volume of conditioned air that flows into the room, thus providing individual control of the room temperature. This type of air distribution system is generally high in efficiency and low in cost because a large number of rooms can be supplied by a single large heating or cooling unit.
The delivery of conditioned air to hospital patient rooms and other "clean" rooms has presented special problems, primarily because patient rooms must be maintained at pressures different from the ambient pressure in adjacent spaces. By maintaining the hospital patient room (or clean room) pressure at a relatively higher level, bacteria and other contaminants are prevented from migrating into the room; conversely, by maintaining the patient room (or clean room) pressure at a relatively lower level, bacteria and other contaminants are prevented from migrating from the room. The need to maintain pressure difference between patient rooms and surrounding spaces has prevented the use of variable air volume systems in the past because such systems normally exhaust as much air as is delivered to the room at design conditions, and a pressure differential cannot be maintained when the variable air volume supply air quantity is reduced. Consequently, hospitals (and other clean room type facilities) have not taken advantage of the recognized operating efficiencies and other benefits of variable air volume air distribution systems. The air delivery systems that are currently used in these applications are only 50-70% as efficient as variable volume systems, and the resulting high energy costs have contributed significantly to the rapid escalation of hospital operating costs.